1. Field of the Invention
The present invention generally relates to an optical detection apparatus and, more particularly, to a reflectance measuring apparatus capable of measuring the reflectance of large-angle reflected light scattered from a sample.
2. Description of the Prior Art
The problems due to global warming have attracted tremendous attention. It is reported that the fossil fuels will be used up in less than 60 years, which leads to raised cost of fossil fuels related products. Therefore, the development in renewable energies has been a key topic of research. The solar energy, being natural and free of pollutions, has become the most commercially competitive one among the renewable energies.
Generally, the solar cell uses an anti-reflecting layer formed thereon to prevent the incident solar beams from being reflected. Since the surface of a silicon wafer is mirror-like and reflects over 30% of the incident solar beams, 30% of the solar energy is lost without the anti-reflecting layer. In addition to the anti-reflecting layer, the surface of a single-crystal silicon solar cell is further textured to reduce reflection of the incident solar beams. The textured surface has a plurality of pyramids, which enable the incident solar beams to experience at least two reflections before escaping from the surface. This decreases the percentage of the incident solar beams being reflected.
In order to measure the reflectance of a localized surface of a solar cell to evaluate the manufacturing quality, U.S. Pat. No. 5,406,367 discloses an apparatus and a method, wherein a light integrating sphere is disposed on a sample to collect large-angle reflected light to be detected by a photo-detector for intensity measurement. However, in this disclosure, the spreading angle is restricted while measuring the spreading angle of the reflected light because the reflected light cannot entirely enter the light integrating sphere if the spreading angle of the reflected light is too large, which leads to measuring error. Even by enlarging the aperture on the light integrating sphere so that the large-angle reflected light can enter the light integrating sphere, measuring error becomes larger because the reflected light inside the light integrating sphere escapes easily through the enlarged aperture.